1. Field of the Present Invention
The present invention is in the field of mechanical devices and more particularly in the field of counterbalanced mechanical arms or extension.
2. History of Related Art
In the field of mechanical systems, mechanisms for counterbalancing a rotating or pivoting arm are found in a wide variety of applications from construction equipment to computer displays. Referring to FIG. 1, an illustration of fundamental counterbalancing concepts is presented. In FIG. 1, a mechanical member or arm 102 is fixed to a pivot point 104. The pivot point 104 is used to define the origin of a Cartesian coordinate system that defines the plane within which mechanical arm 102 is free to rotate. In this illustration, the force of gravity (g) is shown as a vector pointing in the −y direction. For purposes of determining the movement or torque exerted about the pivot point 104 by mechanical arm 102, the arm can be represented as a point mass 106 having a weight of W and positioned at a distance of r1 from pivot point 104. Mechanical arm 102 is free to pivot about pivot point 104. The position of mechanical arm 104 is described by the angle φ. Quantitatively, the movement exerted on the pivot point 104 by arm 102 is r1*cos(φ)*W.
Counterbalancing mechanical arm 102 is achieved in FIG. 1 by providing a counterbalance weight 112 and a counterbalance extension 110 that extends from pivot point 104 collinear with arm 102. Counterbalance weight 112 has a weight C and is located a distance r2 from pivot point 104. Counterbalancing is achieved when the movement exerted about pivot point 104 is equal in magnitude and opposite in direction from the movement exerted by mechanical arm 102. Quantitatively, this state is achieved when r2cos(φ)C=r1cos(φ)W or r2C=r1W. Unfortunately achieving this type of counterbalancing requires the addition of an undesirably long extension piece 110, undesirable additional weight C, or both.
An attempt to address the undesirable weight and size of the counterbalance approach of FIG. 1 is illustrated in FIG. 2. In this counterbalance system, a torsional spring 120 is attached to mechanical arm 102 to produce a counteractive movement on mechanical arm 102. This approach limits the arc in which mechanical arm 102 is free to move and may be balanced in just one or two locations as the force exerted by spring 120 varies with the position of the arm. Another commonly encountered configuration, as depicted in FIG. 3, employs a linear spring 130 connected between an extension piece 132 of arm 102 and a fixed point to produce a force on the arm. This approach also undesirably limits the movement of mechanical arm 102 and produces a force that only counterbalances the mechanical arm in just one or two positions. It would be desirable to implement a mechanism and assembly that would enable the counterbalancing of a mechanical arm. It would be further desirable if the implemented mechanism permitted complete freedom of movement of the mechanical arm. It would be still further desirable if the implemented solution was statically balanced independent of the position of the mechanical arm.